For example, Patent Document 1 discloses a conventional fuel injection valve. In the fuel injection valve disclosed in Patent Document 1, a nozzle needle is biased in a closing direction with fuel pressure in a control chamber. The fuel injection valve is configured to control pressure in the control chamber to control a valve operation of the nozzle needle.
More specifically, a control chamber communication passage is formed to communicate with the control chamber regularly. In addition, fuel is discharged from the control chamber through the control chamber communication passage and an exhaust passage to a low-pressure portion thereby to reduce fuel pressure in the control chamber. In this way, the nozzle needle is moved in the opening direction. To the contrary, high-pressure fuel is drawn from a high-pressure passage through the control chamber communication passage into the control chamber thereby to increase fuel pressure in the control chamber. In this way, the nozzle needle is moved in the closing direction.
A valve element is located in a valve chamber to control communication between the control chamber communication passage and the exhaust passage and to control communication between the control chamber communication passage and the high-pressure passage. The valve element is biased with a valve element spring in a direction to block the control chamber communication passage from the exhaust passage. In addition, the valve element is actuated with an actuator, which uses a piezoelectric element, in a direction to block the control chamber communication passage from the high-pressure passage.
It is noted that, a needle closing speed may be desirably set at a high speed in order to retain an accuracy of a quantity of fuel injection. It is further noted that, the needle closing speed may be set at a high speed by enlarging a passage area of a throttle formed in the high-pressure passage.
However, in a state where the control chamber communication passage is blocked from the high-pressure passage, namely, in the needle closing state, pressure of high-pressure fuel produces a force applied to the valve element in a direction to communicate the control chamber communication passage with the high-pressure passage. Therefore, in a case where the passage area of the throttle of the high-pressure passage is enlarged, an area of the valve element, which receives pressure of high-pressure fuel, becomes large in a state where the control chamber communication passage is blocked from the high-pressure passage. Consequently, this configuration may require the actuator to produce a large actuating force to cause the valve element to retain the state where the control chamber communication passage is blocked from the high-pressure passage. Thus, this configuration may enlarge the actuator.
In consideration of this, the fuel injection valve disclosed in Patent Document 1 is configured to utilize pressure in the valve chamber and the control chamber as an assist pressure when the valve element blocks the control chamber communication passage from the high-pressure passage. In this way, this configuration may reduce actuating force required to the actuator. This configuration may enable to avoid enlargement of the actuator and may increase the needle closing speed.
(Patent Document 1)
Publication of unexamined Japanese patent application No. 2006-46323
It is further noted that, it is assumable that a common rail pressure, which is pressure of high-pressure fuel, becomes greater than a present pressure to improve a combustion performance and/or the like. It is further assumable that a passage area of the throttle of the high-pressure passage is further enlarged. Consequently, in those cases, an actuating force required to the actuator may become greater than a present actuating force. Thus, enlargement of an actuator may be unavoidable.